(1) Field of the Invention
This invention relates to a substrate heat treatment apparatus for heat-treating substrates such as semiconductor wafers, glass substrates for liquid crystal displays, glass substrates for photomasks and substrates for optical disks (hereinafter simply called “substrates”). More particularly, the invention relates to a technique for heat-treating a substrate as sucked in a position slightly spaced from a heat-treating plate.
(2) Description of the Related Art
With an increasingly fine line width of patterns formed on substrates today, the requirements for line width uniformity have become stringent, which has led to a strong demand for temperature uniformity in baking treatment in photolithography, especially in baking treatment after exposure (PEB: Post Exposure Bake). However, with enlarged substrate sizes, increased curvatures of substrates take place in the semiconductor manufacturing process. It is difficult to satisfy the requirements for temperature uniformity in a proximity heating mode that heats each substrate only by placing the substrate as separated by a minute space from a heat-treating plate.
Thus, a suction bake mode has been proposed in order to perform uniform heat treatment even for curved substrates. This type of apparatus includes a heat-treating plate with a heater, support elements and a sealer arranged on the upper surface of the heat-treating plate, exhaust bores for exhausting gas, and perforations for receiving transfer pins (as disclosed in Japanese Unexamined Patent Publication H10-284360 (1998), for example). As the transfer pins are driven up and down to transfer a substrate introduced into the apparatus to the support elements, the sealer as well as the support elements contacts the substrate. The sealer then closes lateral areas of a space formed between the substrate and heat-treating plate. The substrate is sucked by exhausting gas through the exhaust bores. By sucking the substrate in this way, any curvature of the substrate is corrected whereby the substrate is heated uniformly.
The conventional apparatus noted above has the following drawback.
The perforations are in communication with the space formed between the substrate and heat-treating plate and closed by the sealer. Since the transfer pins move up and down inside these perforations, it is difficult to seal the space and its gastightness can be lost. In this case, the pressure in the space does not become a negative pressure even when gas is exhausted through the exhaust bores, thereby failing to suck the substrate and correct the curvature. As a result, the substrate cannot be heat-treated properly.